xv A PLAGUE OF VOLES 477 They have, in the case of the first three, transverse ridges, from which stand up two sharp and long tubercles. The other teeth have two ridges. The incisors axe pale yellow. The shape of the teeth and the smallness of the caecum suggest that this Rodent is not so purely a vegetarian as others, and that it nourishes itself largely upon insects. Sub-Fam. 8. Microtinae.—The Voles or Water-Bats form a distinct group of Murine animals, to which the sub-family name of Microtinae has been applied from the genus Microtits (more generally known as ^irvwoltz), a genus which includes the Water-Hat and Ifleld-Voles of this country. This genus has short ears, and a short and hairy tail. Its build is stouter and clumsier than that of the Hats. The genus is confined to the Palaearctic and the ISTearctic regions. In this country there are three species. The best known is the Water- Vole or Water-Hat, M. amphibius, which has been seen by most people, and which frequents streams, ponds, and canals. The feet, curiously enough, are not webbed, -which seems to argue the recent adoption of an aquatic life. Mr. Trevor- Battye has remarked that this animal, when swimming at leisure, uses its hind-limbs only, carrying the fore pair at the sides like a Seal. The Bank-Vole, M. glareolus, is rather a local species in this country. It is a terrestrial Vole, and burrows. The Field-Vole, M. agrestis, has became notorious on account of the "plagues," to which its immense numbers have on occasions given rise. It is the smallest species, and has a greyish-brown fur like the Water-Vole, the Bank-Vole being redder. To give an idea of the cost of the depredations of this animal, Mr. Scherren quotes * a farmer who gave evidence before the Agricultural Commission to the effect that, putting the damage of one Vole at two pence, the amount of loss suffered on a farm of 6500 acres in two years would "be £50,000 S The genus Fiber comes very near the last. It is a North American genus. The hind-feet are slightly webbed; the tail is a trifle shorter than the body, and is compressed and scaly, with scattered hairs. The thumb is short, but with a fully-developed claw. As in the last genus, the small and large intestines are roughly of the same length, and the caecum is about one-fourth of the length of either. It is known as the " Musquash.** 1 Popular NaAwrOfl History of Animals^ London, 1S98.